Discord ToggleEmbed per Kein

Enhances web-version of Discord client with an ability to have toggle-able embeds. All embedded elements by default will be scaled down and hidden, accompanied by a button that allows you to toggle the state of embedded element back to visible. This extension is best used with Compact Mode.

A few notes:

- Recommended Firefox Quantum
- Known issue: embedded elements will have no button in search panel if you return to remembered search panel state through Guild switching (will be addressed)
- Known issue: some spoilers fail to hide button (this is due to nature of how different content-spoilers work; not an issue)